Chapter 1
Basics of Heat Transfer
Chapter 1
BASICS OF HEAT TRANSFER
Thermodynamics and Heat Transfer
11C
Thermodynamics deals with the amount of heat transfer as a system undergoes a process from one
equilibrium state to another. Heat transfer, on the other hand, deals with the rate of heat transfer as well
as the temperature distribution within the system at a specified time.
12C
(a) The driving force for heat transfer is the temperature difference. (b) The driving force for
electric current flow is the electric potential difference (voltage). (a) The driving force for fluid flow is
the pressure difference.
13C
The caloric theory is based on the assumption that heat is a fluidlike substance called the "caloric"
which is a massless, colorless, odorless substance.
It was abandoned in the middle of the nineteenth
century after it was shown that there is no such thing as the caloric.
14C
The
rating
problems deal with the determination of the
heat transfer rate
for an existing system at
a specified temperature difference. The
sizing
problems deal with the determination of the
size
of a
system in order to transfer heat at a
specified rate
for a
specified temperature difference
.
15C
The experimental approach (testing and taking measurements) has the advantage of dealing with
the actual physical system, and getting a physical value within the limits of experimental error. However,
this approach is expensive, time consuming, and often impractical. The analytical approach (analysis or
calculations) has the advantage that it is fast and inexpensive, but the results obtained are subject to the
accuracy of the assumptions and idealizations made in the analysis.
16C
Modeling makes it possible to predict the course of an event before it actually occurs, or to study
various aspects of an event mathematically without actually running expensive and timeconsuming
experiments. When preparing a mathematical model, all the variables that affect the phenomena are
identified, reasonable assumptions and approximations are made, and the interdependence of these
variables are studied. The relevant physical laws and principles are invoked, and the problem is
formulated mathematically. Finally, the problem is solved using an appropriate approach, and the results
are interpreted.
17C
The right choice between a crude and complex model is usually the
simplest
model which yields
adequate
results. Preparing very accurate but complex models is not necessarily a better choice since
such models are not much use to an analyst if they are very difficult and time consuming to solve. At the
minimum, the model should reflect the essential features of the physical problem it represents.
11
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Chapter 1
Basics of Heat Transfer
Heat and Other Forms of Energy
18C
The rate of heat transfer per unit surface area is called heat flux
q
. It is related to the rate of heat
transfer by
∫
=
A
dA
q
Q
.
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 Spring '11
 ENgel
 Dynamics, Thermodynamics, Energy, Heat, Heat Transfer, T Tout

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